Low-oxidation state cobalt-magnesium complexes: ion-pairing and reactivity

Magnesium cobaltates ((Ar)nacnac)MgCo(COD)(2) (1-3) were synthesised by reacting ((Ar)nacnac)MgI(OEt2) with K[Co(eta(4)-COD)(2)] (COD = 1,5-cyclooctadiene) [(Ar)nacnac = CH(ArNCMe)(2); Ar = 2,4,6-Me-3-C6H2 (Mes), 2,6-Et-2-C6H3 (Dep), 2,6-iPr(2)-C(6)H(3)Mes (Dipp)]. Compounds 1-3 form contact ion-pairs in toluene, while solvent separated ion-pairs are formed in THF. The effect of ion-pairing on the reactivity is illustrated by reaction of 2 with tert-butylphosphaalkyne, which affords distinct 1,3-diphosphacyclobutadiene complexes. The heteroleptic sandwich complex [((Dep)nacnac)MgCo(P(2)C(2)tBu(2))](2) (4) is selectively formed in toluene, while the homoleptic bis(1,3-diphosphacyclobutadiene) complex [((Dep)nacnac)Mg(THF)(3)][Co (P(2)C(2)tBu(2))(2)] (5) is obtained in THF. Complex 4 is a precursor to further unusual phosphaorganometallic compounds. Substitution of the labile COD ligand in 4 by white phosphorus (P-4) enabled the synthesis of the phosphorus-rich sandwich compound [((Dep)nacnac)MgCoP4(P(2)C(2)tBu(2))](2) (6). The heterobimetallic complex (Cp*NiP(2)C(2)tBu(2))Co(COD) (7) was isolated after treatment of 4 with Cp*Ni(acac) (Cp* = C5Me5, acac = acetylacetonate).

Automated summary

The synthesis and reactivity of magnesium cobaltates were studied, revealing the formation of different types of ion pairs under different solvent conditions which influenced the reactivity. Experimental results showed that the sandwich complexes can serve as precursors for the preparation of unconventional organometallic phosphorus compounds, demonstrating the substitution of some COD ligands.